A. The eosinophil ribonucleases. Eosinophil cationic protein (ECP) and eosinophil-derived neurotoxin (EDN) are granule proteins with structural and functional homology to members of the mammalian ribonuclease gene family. We have determined that the genes encoding EDN and ECP have accumulated non-silent mutations at rates exceeding those of all other functional coding sequences studied in primates, while retaining both the structural and catalytic components required for ribonuclease activity (Rosenberg et al (1995) Nature Genetics 10: 219-223), and that evolutionary constraints have promoted two novel functions--both cytotoxicity and enhanced ribonuclease activity--in the two human members of this gene family. (Rosenberg and Dyer (1995) J. Biol. Chem. 270: 21539-21544); these studies have set clear parameters for the study of the host defense-related activities of these eosinophil proteins. B. Identification and characterization of novel human ribonucleases. We have provided a molecular characterization of human ribonuclease 4 (Rosenberg and Dyer (1995) Nuc. Acids Res. 23: 4290-4295), a ribonuclease released from activated human monocytes. We have identified and characterized a completely novel ribonuclease (RNase k6) which is most similar in sequence to human EDN, and expressed in human monocytes and neutrophils (Rosenberg and Dyer (1996) In review). C. Eosinophilopoiesis. We have determined that optimal expression of the genes encoding both EDN and ECP requires interaction between promoter and single intron of each gene (Tiffany et al. (1996) J. Biol. Chem. 271: 12387-12393, Handen et al. (1996) In review). The crucial intronic element was found to be a consensus sequence for the transcription factor NFAT-1 (Handen and Rosenberg (1996) In review), a factor that was not previously known to participate in regulating the expression of myeloid genes. We will determine whether NFAT-1 or a related transcription factor participates in the transcriptional regulation of these and related eosinophil genes. D. The eosinophil Charcot-Leyden crystal (CLC) protein. We have characterized the beta-galactoside binding activity of this protein (Dyer and Rosenberg (1996) Life Sci. 58: 2073-2082), and determined that its gene structure is similar to that of the galectin family of beta-galactoside binding proteins as well (Dyer et al. (1996) In review); natural ligands of CLC will be identified.